History is the basis for our interpretation of humanity's past. Indeed, new developments in digital humanities and the digitalization of archives can place historical sources in a new light. Systematized historical sources allow us to see the practical changes that have occurred over centuries of ethnobotany and analyze (although sometimes solely hypothesize on) the causes of such changes. Studying history helps us to understand the influences on the evolution of local ecological knowledge regarding plant use. In ethnobotany, numerous understudied historical sources await modern interpretations. Old uses enhanced by the new possibilities offered by modern technology can enrich our everyday lives. Yet understanding historical sources, especially in ethnobotany, where several disciplines are involved, is not univocal. Mistakes introduced by misidentified plants or information misinterpreted from old languages can have negative, long-term consequences. This Reprint of the 2nd edition of the Special Issue aims to provide examples of the critical analysis of various historical sources, provide insights into ongoing historical and diachronic studies on plant use, and introduce the best-practice guidelines for interpreting such data.